The policy is almost like Aviance GirlUK say's but more definely is:
No flying 48 hours after the cast has been put on, after that you can.
(Because of swelling, tis can cause greater risk of DVT
But you can fly immediately after the cast has been put on if it is a split cast or a slab cast. (Thats like a half cast or a full cast which as been split in the middle when the cast was put on)
This is what I was taught at BA
and is also the same at the other charter companies I have worked for.